Dendrimers are polymers with a narrow molecular weight distribution that have a highly branched structure which elaborates radially from a single core. Dendrimers are characterized by a low viscosity, high reactivity, high solubility, and low glass-transition temperature and as a consequence their applications have been the subject of study. The following are examples of the already known organosilicon dendrimers: siloxane dendrimers (refer to Rebrov et al., Dokl. Acad. Nauk. SSSR, 309, 367 (1989) and Masamune et al., J. Am. Chem. Soc., 112, 7077 (1990)), carbosiloxane dendrimers (refer to Kakimoto et al., Macromolecules, 24, 3469 (1991); Japanese Published Patent Application (Kokoku or Examined) Number Hei 7-17981 (17,981/1995); and Sheiko et al., Macromol. Rapid Commun., 17, 283 (1996)), and carbosilane dendrimers (refer to Roovers et al., Macromolecules, 26, 963 (1993) and Japanese Published Patent Application (Kokoku or Examined) Number Hei 8-311205 (311,205/1996)). This literature also discloses carbosiloxane dendrimers in which the siloxane bond and silalkylene bond occur in alternation (refer to Japanese Published Patent Application (Kokoku or Examined) Number Hei 7-17981 and Sheiko et al., Macromol. Rapid Commun., 17, 283 (1996)). However, the carbosiloxane dendrimers disclosed therein are limited to dendrimers in which the starting reagent that forms the dendrimer core is a silane compound bearing a plural number of vinyl or allyl groups bonded to a single silicon atom, and the methods disclosed therein can only produce low-molecular-weight dendrimer at a low number of generations. The synthesis by a one-step polymerization method of highly branched polymer in which the siloxane bond and silalkylene bond alternate has also been disclosed (refer to Mathias et al., J. Am. Chem. Soc., 113, 4043 (1991)), but this method cannot produce dendrimer with a narrow molecular weight distribution. In sum, then, there has yet to appear carbosiloxane dendrimer that has a highly branched structure in which the siloxane bond and silalkylene bond alternate, that can also be prepared in a high-molecular-weight form, and that exhibits a narrow molecular weight distribution.
Organosilicon polymers containing a plural number of silicon-bonded hydrogen atoms in each molecule are used as crosslinkers in hydrosilylation-based crosslinking reactions and as precursors for the synthesis of functional organosilicon polymers. Desire has recently arisen for the development of novel crosslinkers that can exhibit a high crosslinking efficiency and can generate cured products having excellent properties (e.g., mechanical strength, adhesiveness, and durability) and for the development of novel precursors that would lead to the synthesis of functional organosilicon polymers with unique reactivities. In addition, organosilicon polymers containing a plural number of silicon-bonded alkoxy groups in each molecule are known to be useful as coatings, as starting materials for paint vehicles, and as crosslinkers for moisture-curing compositions. In this case again desire has recently arisen for the development of highly reactive organosilicon polymers that would be useful for improving end-product performance, such as mechanical strength, adhesiveness, and durability. The functional groups bonded at the branch terminals of a dendrimer as a general rule are highly reactive, and in addition a narrow molecular weight distribution can be expected to generate a uniform reactivity. Accordingly, dendrimer bearing the aforementioned reactive groups at its branch terminals would be well-suited for satisfying the desires alluded to above.
The present inventors developed the present invention as a result of extensive investigations directed to solving the problems described above. In specific terms, the object of the present invention is to provide a novel carbosiloxane dendrimer that has a highly branched structure in which the siloxane bond and silalkylene bond alternate and that contains silicon-bonded hydrogen and/or silicon-bonded alkoxy.